VBA loop preference - excel

Question

I am currently trying to optimize a VBA code with extreme execution time (56 hours and more on high end PC). The main problem is nested loops (up to 8) due to complicated iterative calculations and referencing ranges in formulas.
I have two questions:
1)
What loops are most preferred in VBA (based on their hardware strain for lack of better word)
2)
Is there a way to reference variable range of cells in a formula? For example in formula:
=AGGREGATE(15,6,SQRT((R2C10:R500000C10-RC[10])^2+(R2C11:R500000C11-RC[11])^2+(R2C12:R500000C12-RC[12])^2),1)
I am referencing relative cell: "R500000C10". There are two main issues: For one, the half milion cells might not capture all data - though in most cases there is less active cells than that, in same cases that might be an issue. Second, it takes forever to scan through so many cells (same reference is used in multiple of VLOOKUPs).
The first issue could be solved by referencing the whole column, but that makes the second problem worst.
I would like to reference it in a similar way that xlDown works:
Range().End(xlDown).Select
The problem there is I would need to reference it within the Active.Cell.FormulaR1C1. Is there a way to do that?
Thanks!

Answer 1

Well you wrote that you have a code with 8 loops and try to optimize it maybe you can edit and put part of that code, because your description is very general, however, with information that you put i speculate that about your point
1)it depend what do you want to do? because each "loop" have their own use for specifyc scenaries
2)there are tricks to do that but all depend what are you trying to do and why you want to use .formulaR1C1
again im speculating but you can try tu separate your loops in indenpendent function, and maybe you are putting a formula inside cells, and question is why? you can create functoins and Sub in your VBA code and do your "extrem execution" without use xtra "resours"